It is known from the literature that the preparation of reactive, uniformly alkalized cellulose and uniformly substituted cellulose derivatives presents great difficulties. According to a well-known and widely used method for the production of alkali cellulose, cellulose fibers or cellulose chips are dipped into solutions of from about 20 to 50% of sodium hydroxide. Excess solution is squeezed off after this dip-alkalization. (See, German Pat. No. 977,104.) In alkalization in mixing systems, the required amount of sodium hydroxide can be adjusted more accurately by spraying, as is set forth in German Published Application (DOS) No. 26 35 403.
However, the two above-described methods yield an irregular distribution of the alkali metal on the cellulose, which distribution is manifested by irregular substitution after reaction with etherifying agents. Such products do not exhibit the readily dissolving properties of uniformly substituted cellulose ethers. In view of these facts, it has been standard procedure to grind the cellulose before alkalization to obtain a large surface area and a high reaction velocity. However, during alkalization, partially alkalized cellulose powder swells considerably and forms lumps so that a homogeneous distribution of the alkali metal hydroxide on the cellulose powder is not ensured. It has been necessary for the alkalization of fibrous or powdered cellulose to use, for example, a screw press, to homogenize and advance the material [German Published Application (DAS) No. 15 43 114] or to work in the presence of an etherifying agent in a mixer [DOS 26 35 403].
While use of a screw press or another pressure device may be suitable under certain circumstances, alkalization in the presence of an etherifying agent, for example, methyl chloride, requires an apparatus capable of containing pressure, since a considerable excess pressure builds up due to the temperature conditions. Under these conditions, a suspension of cellulose powder, sodium hydroxide, and methyl chloride can be produced, as is described in German Published Application (DOS) No. 26 36 935. However, the preparation of such a suspension is not equivalent to the production of a homogeneously alkalized cellulose.